This invention relates to a system for pumping an abrasive or corrosive fluid and, more particularly but not exclusively, is concerned with a system for pumping clay slurry into a high pressure plate filter press.
When supplying slurry to a high pressure filter press, the pumping system used must be capable of delivering slurry at high pressure, for example 1000 p.s.i., with a flow rate which is variable between zero and, for example, 30 liters per second. If slurry is pumped at such high pressures directly by a pump, the abrasive nature of the slurry leads to very rapid seal wear in the pump, and consequently maintenance costs are high. To avoid this wear, it is known to raise the pressure in oil with a reciprocating piston pump which feeds the oil, at each stroke, directly to a transfer vessel where the pressure is transferred to the slurry. On the return stroke of the piston, the oil flows back from the transfer vessel to the cylinder of the pump. This system is incapable of acting satisfactorily at flow rates below 14 liters per second.
Another prior art system is disclosed in U.S. Pat. No. 3,891,352. In that system, an intermediate fluid transmits pressure to the slurry in a transfer vessel. The intermediate fluid is pressurised by a piston which is connected to a further piston, this further piston being reciprocated by a working fluid which is directed under pressure by a changeover valve alternately to one side or the other of the further piston. The changeover valve is actuated by a sensor which is disposed in the transfer vessel and is responsive to the interface between the slurry and the intermediate fluid. This system requires two different fluids apart from the slurry to be pumped. Furthermore, leakage of fluid across the pistons can result in faulty operation.
Other systems are known which do not employ transfer vessels, but in which the fluid, for example water, in which the pressure is raised is allowed to dilute or contaminate the slurry.